1. Field of the Invention
The present invention relates to a paste applicator for drawing a paste film in a desired pattern on a substrate.
2. Description of the Prior Art
There are known technologies of drawing a paste film in a desired pattern on a substrate by changing the relative positional relationship between a nozzle and the substrate up and down, back and forth, right and left while a paste is being discharged through a nozzle provided at an end of a paste reservoir tube. In a technology disclosed in, for example, Japanese Patent Application Laid-Open No.2-52742 (1990), a desired resistive pattern is formed by discharging a resistive paste through a nozzle onto a substrate while the substrate is being relatively moved to the nozzle and the gap between the nozzle and the substrate is being adjusted.
There are some cases where a paste in a paste reservoir tube is almost discharged by drawing a desired pattern, and lack of the paste occurs halfway through drawing a pattern onto the next substrate. In such a case, refilling a paste into the paste reservoir tube at a midpoint in drawing a pattern causes a structural problem as a precise equipment. Therefore, in such a conventional paste applicator described above, the paste reservoir tube is generally exchanged with a new paste reservoir tube filled with paste before starting drawing of the next substrate. In this occasion, the nozzle is also exchanged because the nozzle is constructed in a one-piece structure with the paste reservoir tube. Hereinafter, such exchange is referred to as "nozzle exchange".
In such a case, the relative position of the nozzle discharging port to the substrate before and after the nozzle exchange is varied due to machining accuracy of the paste reservoir tube or the nozzle and variation of assembling accuracy in the nozzle to the paste reservoir tube. As a result, it has been often difficult to draw a paste pattern starting from a desired position on the substrate.
In a case of drawing, for example, a sealing material in a pattern onto a liquid crystal sealing substrate of a liquid crystal display apparatus, if any positional displacement exists in the pattern of the sealing material, a part of display pixels may be placed outside the pattern of the sealing material and consequently a correct picture cannot be displayed on the screen.
Technologies similar to the above are also disclosed in U.S. Pat. No. 5,415,693 and U.S. Pat. No. 5,437,727 which are invented by the some of inventors of the present invention.